TM 11-5805-424-15/NAVELEX 0967-220-9010/TO 31W2-2G-41
window timer, and a positive input to
approximately 0.75 second (adjustable by TALK
transistor Q5 in the window timer.
REQUEST WINDOW control resistor 1A1R10). If the
receive carrier alarm is actually a talk request, with a
(b) If the alarm condition does not remain for
duration of 1.5 second, both the initial timer and the
approximately 1 second, the circuits are
window timer are allowed to time out, lighting the front
reset to the original no-alarm condition
panel TALK REQUEST indicator lamp.
((1) above), and capacitor C1 discharges
b. Initial Timer.
through conducting transistor Q2.
c. Window T7imer.
(1) With a carrier signal being received by amplifier
IN-16, the negative input holds transistor Q1
(1) Initially, in the no-alarm condition, transistor Q5
conducting, thereby applying a ground to the
is conducting so that transistor Q6 conducts; this
input of transistor Q2. Transistor Q2 therefore
action prevents capacitor C2 from charging and
conducts and Prevents capacitor C1 from
transistor Q7 is held cut off. Circuit component
charging. Diode CR2 is reverse-biased and
functions for the window timer are essentially
holds transistor Q3 cut off, so that +15 volts is
the same as for the initial timer (b(2) above).
applied to the base of transistor Q4 keeping
(2) Approximately 1 second after an alarm
transistor Q4 cut off.
condition occurs, collector supply voltage is
(2) Resistors R2 and R3 provide initial bias for
applied to transistor Q7 from the initial timer
transistor Q1, and resistors R4 and R5 form the
(b(3) above). The positive voltage applied to
dc coupling circuit for transistor Q2. Diode CR1
transistor Q5 cuts off transistor Q5;
provides the emitter resistance, and resistor R6
consequently transistor Q6 is held cut off,
is a collector load resistor. Diode CR2 and
allowing capacitor C2 to charge toward +15
resistor R8 establish a positive feed through
volts through TALK REQUEST WINDOW
voltage level for transistor Q3, resistor R9 is the
control resistor 1A1R10. When capacitor C2
collector load resistor, and resistor R10 provides
charges sufficiently (in approximately 0.75
dc coupling between transistors Q3 and Q4.
second, as determined by TALK REQUEST
WINDOW resistor 1A1R10), transistor Q7
(3) When a talk-request (or carrier alarm) condition
conducts, placing a ground on the input of
occurs, a ground is applied, through pin H, to
amplifier IN-17, to cut off transistor Q8. If the
amplifier IN-16 and to diode CR6 of AND gate
alarm signal is actually a talk-request, the
GAD-3. The ground passed by diode CR6 cuts
positive input to diode CR6 of AND gate GAD-3
off amplifier IN-18, which does not affect
is removed after 1.5 second. With diode CR5
bistable FFB-1. However, the ground fed to
reverse biased by the -15 volts applied from
amplifier IN-16 cuts off transistor Q1;
amplifier IN-17, AND gate GAD-3 is inhibited,
consequently, transistor Q2 is cut off, allowing
allowing amplifier IN-18 to conduct (due to
capacitor C1 to charge toward +15 volts through
current flow through resistors R22, R23, and
DELAY control resistor 1A1R9.
R24). With transistor Q9 conducting, a positive
(a) If the alarm or talk-request signal persists
input transition (-15 volts to ground) is applied
for longer than 1 second (determined by
through coupling capacitor C4 and diode CR7 to
resistor 1A1R9), the charge built on
trigger bistable FFB-1; this action turns off
capacitor C1 is passed through diode
transistor Q11, which in turn causes transistor
CR2,
biasing
transistor
Q3
into
Q12 to conduct and apply a ground to light the
conduction. This action causes transistor
TALK REQUEST lamp.
Q4 to conduct and supply a positive
collector potential to transistor Q7 in the
Change 5
5-14
